In looms of this type, it is well known to provide in the path of the weft thread, between the bobbin located on one side of the machine and constituting the weft reserve, on the one hand, and the insertion nozzle, on the other hand, a predelivery and measuring device which stores cyclically a length of weft which is predetermined in accordance with the width of the fabric and which allows this length of weft stored provisionally to be drawn off at one go at the time of insertion.
More particularly, French Patent Publication No. 2,465,812 (French application 80-20,416) discloses a weft predelivery and measuring device in which a tubular member is connected to a rotary shaft passing through which is an axial channel facilitating the arrival of the weft and its passage into the said tubular member, for winding it around a drum of adjustable peripheral dimensions which is prevented from rotating, means being provided for retaining a predetermined number of turns of yarn wound around said drum and in order to release these turns periodically.
In this weft predelivery and measuring device, which uses the principle of winding on a fixed drum by means of a rotary member making it possible to deposit tangentially the desired number of turns, the length of these turns, and, therefore, the length of yarn stored before being drawn-off in order to effect the insertion of the weft, is made adjustable by providing that the winding drum comprises a radially fixed part, inside which are mounted the means for retaining and releasing the desired number of turns and a part constituted by radially adjustable members. The drum which results from this arrangement comprises, with respect to the axis of the device, a periphery which is more or less eccentric depending on the reduction in the width of the fabric with respect to the maximum width (warping). This eccentric arrangement causes a weft tension which varies according to a substantially sinusoidal law and creates a jerky movement at the time of pulling of the weft.
Moreover, in the above mentioned known device, the means for retaining and releasing the desired number of turns comprise an epicycloidal gear train, making it possible to drive spindles in a circular movement while keeping the spindles in a constant orientation, this epicycloidal train itself being driven by the rotary shaft supporting the radial tubular member through which the yarn passes. This drive includes a worm, a worm gear and an endless belt or chain passing over a driving pinion and over a receiving pinion. The arrangement constitutes a complex mechanism, comprising numerous pinions, shafts and bearings, the production and assembly of which are difficult in view of the small dimensions of the part inside which they are to be fitted. In addition, the design of this mechanism precludes any adjustment of the trajectory of the spindles for retaining turns and it is precisely for this reason that the drum is composed of a radially fixed part enclosing said mechanism and of a part constituted by radially adjustable members.